Range Of External Magnetic Fields Research Articles

Field-driven conversion of two-dimensional solitonic magnetic textures

Magnetic skyrmions and bimerons, characterized by their topological properties and low current-induced motion, are promising magnetic textures for spintronic (skyrmionic) applications. In this work, through atomistic simulations and micromagnetic analysis, we investigate the field-driven manipulation and conversion of skyrmions into bimerons. By applying an in-plane magnetic field, we observe a smooth transition from skyrmions to bimerons, evidencing the persistence of the soliton topology over a wide range of external magnetic fields. Additionally, we obtain a state diagram elucidating the dependence of nucleated topological textures on material parameters and in-plane magnetic field strength.

Dynamics of quantum coherence and nonlocality of a two-spin system in the chemical compass.

In this paper a system consisting of two electron spins has been prepared initially in a singlet state using the chemical compass model is considered. It is assumed that each electron spin interacts symmetrically and/or asymmetrically with its respective private nuclear environment in the presence of an external magnetic field. We discussed the effect of the interaction parameters and the external magnetic field on some quantifiers of quantum correlations as entanglement, coherence, Bell inequality, as well as the steerability inequality. It is shown that within a certain range of external magnetic fields, the quantum coherence and entanglement behave similarly. The Bell and the steerable inequalities predicted a similar behavior for symmetric and asymmetric interactions. Moreover, as one increases the external magnetic field, the lower bounds of both inequalities have improved. The usefulness of using the spin state as quantum channel to teleport a two-qubit system has examined where the Bell inequality could be above its classical bounds by controlling the interaction parameters. It is shown that by tuning the coupling parameters the fidelity of the teleported state exceeds the classical bounds, as well as the long-lived stationary fidelity could be achieved during the interaction time.

Ultrafast heat-assisted magnetization dynamics in a ferrimagnetic insulator

Ultrafast laser-induced heating of ferrimagnetic iron garnet in an external magnetic field triggers magnetization precessional dynamics with a large amplitude. The dynamics is studied as a function of magnetic field, laser fluence, and sample temperature. Exploring the three-dimensional space of these parameters experimentally and computationally, we identify the conditions for which the amplitude of the precession is the largest and even achieves values sufficient for magnetic recording. We found that the range of external magnetic fields and temperatures, which corresponds to the magnetic recording, is rather narrow. Modeling the dynamics, using magnetization as a macroscopic parameter, reveals that this range of parameters is defined by the optimal height of the potential barrier separating two stable states. The barrier needs to be low enough to allow the switching but not so low that the stability of the states is lost.

Current-assisted magnetization reversal in Fe3GeTe2 van der Waals homojunctions.

Among the numerous two-dimensional van der Waals (vdW) magnetic materials, Fe3GeTe2 (FGT), due to its outstanding properties such as metallicity, high Curie temperature and strong perpendicular magnetic anisotropy, has quickly emerged as a candidate with the most potential for the fabrication of all-vdW spintronic devices. Here, we fabricated a simple vertical homojunction based on two few-layer exfoliated FGT flakes. Under a certain range of external magnetic fields, the magnetization reversal can be achieved by applying a negative or positive pulse current, which can reduce the coercivity through the spin orbit torque of FGT itself in addition to the Joule heat. Moreover, the asymmetrical switching current is caused by the spin transfer torque in the homojunction. As the temperature increases, the magnetization reversal can be observed at a smaller external magnetic field. Our demonstrations of the current-assisted magnetization reversal under a magnetic field in all-vdW structures may provide support for the potential application of vdW magnetism.

Noncollinear Remanent Textures Induced by Surface Spin Flop in Synthetic Antiferromagnets with Perpendicular Anisotropy

The surface spin flop, observed in synthetic antiferromagnets (SAFs) with uniaxial anisotropy and strong antiferromagnetic (AF) interlayer exchange coupling, can be considered as a laterally homogeneous, vertical AF domain wall pushed into the SAF from either the top or the bottom in the presence of a strong external vertical magnetic field. As a result, the AF domain wall can be described as a one-dimensional entity. In this work, we present a concept to stabilize laterally homogeneous vertical AF domain walls by local variation of the perpendicular magnetic anisotropy in $\mathrm{Co}/\mathrm{Pt}$-based SAFs. Our approach not only allows the stabilization of the vertical AF domain wall in the absence of any external magnetic field, but furthermore enables a deterministic selection among four different remanent states, each one stable within a broad external magnetic field range of almost one tesla. We also demonstrate an extension to our concept by stabilizing two coexisting vertical AF domain walls, thus yielding a system with a total of six different selectable (and reprogrammable) remanent states. The controlled stabilization of noncollinear AF textures in the form of vertical AF domain walls at remanence could be used as an infrastructure for propagating spin waves within the AF domain wall itself, as well as for tuning the dynamic behavior of perpendicular standing spin wave modes existing vertically across the SAF.

Magnetic skyrmions generation and control in FePt nanoparticles through shape and magnetocrystalline anisotropy variation: a finite elements method micromagnetic simulation study

Magnetic skyrmions created during magnetization reversal in cylindrical, reuleaux and polygon-based magnetic nanoparticles with perpendicular magnetocrystalline anisotropy (MCA) similar to that of partially chemically ordered FePt were studied using finite elements method micromagnetic simulations. Néel chiral stripes, horseshoe, labyrinth skyrmionic textures along with multiple skyrmions were unveiled in different systems generated by the variation of the MCA magnitude and the nanoparticles geometrical shape. These skyrmionic textures under certain conditions can be stable in a range of external magnetic fields and for different MCA values. Simulations revealed the inherent relation of skyrmionic states with nanoparticle geometry and the energy differences between successive external field values observed during the magnetization reversal process. Energetical transitions from non-skyrmionic to skyrmionic and from skyrmionic to different skyrmionic states were quantified and associated with the individual anisotropy, exchange and demagnetization energy contributions for the nanoparticles studied. Finally, the diameters of Néel type skyrmions created through the nanoparticle shape variation were reported for different MCA and external magnetic field values.

An automated measuring complex of electromagnetic parameters of materials in the field of superhigh frequencies

This work is dedicated to the features of measuring the electromagnetic parameters of materials. In the field of superhigh frequencies, there are practically no documents regulating the requirements for the properties of materials and means for measuring the electromagnetic parameters of materials. To solve the problems of metrological support for this frequency range and new materials, several steps are required. One of them is the development of a measuring complex. This work describes the composition of the developed model of such a complex and its distinctive features. The text contains models of materials. The extended frequency ranges from 200 MHz to 80 GHz. The range of external magnetic fields has been expanded from 4 kA/m to 70 kA/m.

Experimental investigation on the thermophysical properties of low concentration magnetic colloidal suspensions (nanofluids) with the variations in temperature & magnetic field

The experiments are conducted to investigate the effect of temperature, magnetic field, and nanoparticles on the effective thermophysical properties (thermal conductivity, viscosity and density) of the magnetic nanofluids. The Fe3O4 magnetic nanoparticles are dispersed in the water at various concentrations and the resulted suspensions are assessed in the temperature range 10–70°C and under the presence of an external magnetic field range from 0 to 750 Gauss. The different parameters have observed the significant effects on the thermal conductivity, viscosity and density of these colloidal suspensions. The experiments have revealed that the thermal conductivity is enhanced with nanoparticle concentration, temperature and magnetic field. The new empirical correlations using Buckingham-Pi theorem and analytical approach have been proposed and discussed comprehensively for the effective thermal conductivity for such magnetic suspensions under the presence of a magnetic field. The viscosity of the colloidal suspension is shown significant enhancement with nanoparticle concentration and decrement with increasing temperature. The empirical correlation for the viscosity is reported and elucidates the temperature dependence of the viscosity. However, the density for these suspensions shows only a trivial enhancement with concentrations.

NMR study of magnetic structure and hyperfine interactions in the binary helimagnet FeP

We report a detailed study of the ground state helical magnetic structure in monophosphide FeP by means of ${}^{31}$P NMR spectroscopy. We show that the zero-field NMR spectrum of the polycrystalline sample provides strong evidence of an anisotropic distribution of local magnetic fields at the P site with substantially lower anharmonicity than that found at the Fe site by M\"{o}ssbauer spectroscopy. From field-sweep ${}^{31}$P NMR spectra we conclude that a continuous spin-reorientation transition occurs in an external magnetic field range of 4 - 7 T, which is also confirmed by specific-heat measurements. We observe two pairs of magnetically inequivalent phosphorus positions resulting in a pronounced four-peak structure of the single crystal ${}^{31}$P NMR spectra characteristic of an incommensurate helimagnetic ground state. We revealed a spatial redistribution of local fields at the P sites caused by Fe spin-reorientation transition in high fields and developed an effective approach to account for it. We demonstrate that all observed ${}^{31}$P spectra can be treated within a model of an isotropic helix of Fe magnetic moments in the ($ab$)-plane with a phase shift of 36$^{\circ}$ and 176$^{\circ}$ between Fe1-Fe3 (Fe2-Fe4) and Fe1-Fe2 (Fe3-Fe4) sites, respectively, in accordance with the neutron scattering data.

Field-stepwise-swept QCPMG solid-state 115In NMR of indium oxide

Experimental and theoretical investigations of indium-115 electric-field-gradient (EFG) tensors of indium(III) oxide, In2O3, have been presented. Field-stepwise-swept QCPMG solid-state 115In NMR experiments are carried out at T ​= ​120 ​K, observed at 52.695 ​MHz, and in the range of external magnetic fields between 4.0 and 6.5 ​T. The spectral simulations yield the quadrupolar coupling constant, CQ value, of 183(2) MHz and the asymmetry parameter, ηQ, of 0.05(5), for In(1), and that of 126(2) MHz and ηQ of 0.86(5) for In(2). Quantum chemical calculations are carried out to provide 115In EFG tensor orientations with respect to the molecular structure. A relationship between operative frequencies and variable ranges of external magnetic fields is briefly discussed for field-swept solid-state 115In NMR.

Quantitative mapping of stray field planar component by tracking singular points in metallic indicator film

In this work we obtained experimental and simulated images of in-plane component of the stray field created by a permanent magnet using indicator film technique and magneto-optical Kerr effect imaging system. The applied uniform magnetic field and the presence of the source singular point leads to the appearance of the saddle point. The increase of magnetic field leads to convergence of the two points and they annihilation at a critical field. If a relatively weak magnetic field comparable to the coercivity is applied, magnetooptical image with noticeable hysteresis is formed. For the external magnetic field range exceeding the coercivity, we demonstrated the possibility to derive the topography of the stray field created by the permanent magnet by tracking the position of the singular points.

Magnon Pairs and Spin-Nematic Correlation in the Spin Seebeck Effect.

Investigating exotic magnetic materials with spintronic techniques is effective at advancing magnetism as well as spintronics. In this work, we report unusual field-induced suppression of the spin Seebeck effect (SSE) in a quasi-one-dimensional frustrated spin-1/2 magnet LiCuVO_{4}, known to exhibit spin-nematic correlation in a wide range of external magnetic field B. The suppression takes place above |B|≳2 T in spite of the B-linear isothermal magnetization curves in the same B range. The result can be attributed to the growth of the spin-nematic correlation while increasing B. The correlation stabilizes magnon pairs carrying spin 2, thereby suppressing the interfacial spin injection of SSE by preventing the spin-1 exchange between single magnons and conduction electrons at the interface. This interpretation is supported by integrating thermodynamic measurements and theoretical analysis on the SSE.

Facile synthesis of magnetic nanoparticles optimized towards high heating rates upon magnetic induction

Abstract Inductively heatable magnetic particles are powerful additives towards smart processes, such as bonding and debonding on demand or self-healing. For the best efficiency, particles are needed which possess the highest possible heating rates/specific absorption rate when being exposed to a magnetic induction field. Herein, a cheap, simple and upscalable precipitation-oxidation assisted aging synthesis route for magnetic nanoparticles is optimized towards yielding a product with high heating rates. In-depth synthesis parameter studies were carried out to understand how the nanoparticle structure can be influenced in a way to yield the best heating rates. This included variation of the precursors chemistries, precipitant concentration, the oxidation and aging conditions as well as the co-doping of the particles with Zn and Co. A correlation between magnetic hysteresis, measured via vibrating sample magnetometry and specific absorption rate of the samples was established and it was demonstrated how crucial it is to select the right range of external magnetic fields in hysteresis measurements in order to achieve reliable and predictable correlations with the specific absorption power and heating rates, respectively. Via the established understanding and the systematic variation, it was ultimately possible to develop a synthesis procedure, yielding ferrimagnetic iron oxide nanoparticles that come with specific absorption rates of up to 1474 W·g−1 (at a magnetic field of 430 Oe at 1013 kHz).

Structural, magnetic and electric properties of ZrO2 tapes decorated with magnetic nanoparticles

Abstract We produced ZrO 2 ceramic tape decorated with magnetic nanoparticles through tape casting technique. The green and sintered magnetic tapes were characterized by XRD, SEM, EDS, magnetic measurements, and I–V curves. We investigated the changes in the structural, magnetic and electrical properties, after the sintering process, and discussed the connections between them. The magnetic properties, performed in a wide range of external magnetic field and temperature, show magnetite phase for the magnetic nanoparticles governing the magnetic and electric properties of the green tape. On the other hand, for the sintered tape, the increase in the hematite phase led to remarkable changes in the magnetic and electrical properties. The electrical characterization reflects the observed changes in the structural properties after the sintering process. Additionally, the main advantages of the ceramic tapes decorated with magnetic nanoparticles reside in the possibility of producing functional thin ceramic materials that are easily moldable for electronic devices applications.

Axion Insulator State in a Ferromagnet/Topological Insulator/Antiferromagnet Heterostructure.

We propose the use of ferromagnetic insulator MnBi2Se4/Bi2Se3/antiferromagnetic insulator Mn2Bi2Se5 heterostructures for the realization of the axion insulator state. Importantly, the axion insulator state in such heterostructures only depends on the magnetization of the ferromagnetic insulator and, hence, can be observed in a wide range of external magnetic fields. Using density functional calculations and model Hamiltonian simulations, we find that the top and bottom surfaces have opposite half-quantum Hall conductances, [Formula: see text] and [Formula: see text], with a sizable global spin gap of 5.1 meV opened for the topological surface states of Bi2Se3. Our work provides a new strategy for the search of axion insulators by using van der Waals antiferromagnetic insulators along with three-dimensional topological insulators.

Magnetopiezofiber

The results of the magnetoelectric effect study in the magnetopiezofiber are presented. Magnetopiezofiber consists of mechanically coupled piezoelectric (one layer of lead zirconate titanate) and magnetostrictive (two metglass layers) fibers. The layers were joined together by epoxy under pressure and heating. The sample active area dimensions were 28x7x0,34 mm. The study of the magnetoelectric effect was carried out in the frequency range from 0 to 150 kHz and external magnetic field range from 0 to 100 Oe. Maximum value of the ME voltage coefficient αE = 62,75 V/cm-Oe was measured on the electromechanical resonance frequency f = 61 kHz with an external magnetic field of 4,5 Oe. Obtained results indicate the prospects of the proposed design in magnetoelectric devices application.

From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents.

Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate and excitation of a magnon supercurrent, propelled by a phase gradient in the condensate wave function, can be observed at room temperature by means of the Brillouin light scattering spectroscopy in an yttrium iron garnet material. We study these phenomena in a wide range of external magnetic fields in order to understand their properties when externally pumped magnons are transferred towards the condensed state via two distinct channels: a multistage Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step kinetic instability process. Our main result is that opening the kinetic instability channel leads to the formation of a much denser magnon condensate and to a stronger magnon supercurrent compared to the cascade mechanism alone.

Tunable surface plasmon resonance polarization beam splitter based on dual-core photonic crystal fiber with magnetic fluid

A tunable surface plasmon resonance based on polarization beam splitter (PBS) is proposed by using a dual-core photonic crystal fiber with magnetic fluid. Propagation characteristics of the PBS are analyzed by finite element method. The resonance wavelength which satisfied the phase matching condition shifts when change external magnetic field. Simulation results show that incident light wavelengths with a wide range of 1.45– $$1.55\,\mu$$ m can be split, the minimum bandwidth of 168 nm and the extinction ratio can reach to − 128 dB when external magnetic field range 400–760 Oe at the same structure.These properties make the splitter we proposed a competitive candidate for fiber beam splitter.

Spin-ice behavior of three-dimensional inverse opal-like magnetic structures: Micromagnetic simulations

We perform micromagnetic simulations of the magnetization distribution in inverse opal-like structures (IOLS) made from ferromagnetic materials (nickel and cobalt). It is shown that the unit cell of these complex structures, whose characteristic length is approximately 700nm, can be divided into a set of structural elements some of which behave like Ising-like objects. A spin-ice behavior of IOLS is observed in a broad range of external magnetic fields. Numerical results describe successfully the experimental hysteresis curves of the magnetization in Ni- and Co-based IOLS. We conclude that ferromagnetic IOLS can be considered as the first realization of three-dimensional artificial spin ice. The problem is discussed of optimal geometrical properties and material characteristics of IOLS for the spin-ice rule fulfillment.

The properties of short-circuited HTSC coils

The properties of short-circuited multiturn superconducting coils have been studied; coils with nonsuperconducting contacts have been fabricated from a high-temperature superconducting (HTSC) tape made by Super Power Company. The magnetic flux captured by HTSC coils has been measured at different values of magnetic field of the magnetizing solenoid. the critical current in the coils have been experimentally determined based on the maximum values of the field they captured. It is ~50% of the nominal value for this HTSC tape. The range of external magnetic field, where HTSC coils keep the captured magnetic flux, has been experimentally found. The obtained results have demonstrated the possibility of designing magnet systems with levitating coils made of HTSC tape, in which levitation is controlled without using feedbacks.